1. Field of the Invention
The present invention relates to a digital camera capable of focus adjustment by a manual operation while seeing an image of an electronic viewfinder, and a focus control method in the digital camera.
2. Description of the Related Art
In general, in a method for manual focusing (MF) in a digital camera, a user operates to rotate a forced adjustment ring (focus ring) of a lens barrel to move a taking lens. The user then observes a subject, seeing a finder or an electronic viewfinder (EVF) under movement of the taking lens, to stop the taking lens at a lens position where it is determined that focusing is completed. In this operation method of MF, the user cannot always stop the taking lens at an optimum focusing position depending on the user's performance, viewability of the finder, and the like.
Meanwhile, in auto-focusing (AF) in the digital camera, the taking lens is automatically moved, and predetermined calculation is performed on an output signal from an imaging element when the taking lens is moved, whereby an evaluation value (hereinafter referred to as focus evaluation value) representing a focusing level is calculated. The taking lens is moved to a lens position where the focus evaluation value exhibits the peak, whereby the optimum focusing position is provided.
The focus evaluation value represents a magnitude of a high frequency component of an image signal, which is output from the imaging element when a subject is taken. As the taking lens is closer to the focusing position, the focus evaluation value shows a higher value. Thereby, in AF, a position of the taking lens where the focus evaluation value is the peak value is searched, whereby the taking lens can be adjusted at the optimum focusing position. AF is referred to as, for example, mountain-climbing AF, imager AF, or contrast AF. In the invention, AF is referred to as imager AF.
There is a well-known technique for reducing a time required for focusing and improving focusing accuracy by combining MF with imager AF. For instance, in Jpn. Pat. Appln. KOKAI Publication No. 2002-107609, the taking lens is operated to be moved from a non-focusing position to a focusing position by MF. At this time, the focus evaluation value is calculated by imager AF. When the focus evaluation value changed beyond a predetermined threshold value, the focusing operation is switched from MF to AF, and then focusing is performed. Namely, focusing is finally performed by AF. In Jpn. Pat. Appln. KOKAI Publication No. 2002-107609, it is possible to realize more accurate focusing than general focusing by MF, and, at the same time, to reduce the time required for focusing.
Meanwhile, a technique using the focus evaluated value in a process for focusing by MF is well-known. For instance, Jpn. Pat. Appln. KOKAI Publication No. 6-113184 discloses a camera apparatus which displays a level of a focusing state in real time. Jpn. Pat. Appln. KOKAI Publication No. 2001-42207 discloses an electronic camera which displays information of a position of the taking lens and displays information of the focus evaluation value with a bar. Jpn. Pat. Appln. KOKAI Publications Nos. 6-113184 and 2001-42207 clarify the focusing level to a user, and, at the same time, realize MF relatively more accurate than general MF.
In addition to the well-known techniques for obtaining the focusing state in a digital camera, the background art of the conventional lens interchangeable camera will be described hereinafter.
In the lens interchangeable camera, an interchangeable lens can be attached thereto and detached therefrom. Such an interchangeable lens has been sold from the times of film cameras. As the current lens interchangeable camera, there is a single-lens reflex digital camera, for example. The focus detection by AF in the single-lens reflex digital camera is mainly performed by TTL phase difference AF, for example.
As the previous film camera, there is a single-lens reflex camera. The focus detection in the single-lens reflex camera has adopted a TTL phase difference AF system, for example. Thereby, the lens drive system on the interchangeable lens side is designed optimally for an AF system.
Namely, the lens drive system on the interchangeable lens side in any camera adopts the TTL phase difference AF system, for example. In the TTL phase difference AF system, a subject image is divided into a plurality of light paths, and thus two subject images are obtained. A defocus amount of the taking lens is then detected by using deviation between those subject images, and thus the taking lens is driven by a lens drive amount corresponding to the defocus amount. Thereby, the taking lens is adjusted at the focusing position. As a lens driving actuator, for example, a direct current (DC) motor or ultrasonic (US) motor is generally used.